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Publication An alternative to the igneous crust fluid plus sediment melt paradigm for arc lava geochemistry(2024) Turner, Stephen; Langmuir, Charles HA long-standing paradigm of arc geochemistry is that the trace element compositions of arc lavas arise from two compositionally distinct slab components: an aqueous dehydration fluid from the subducting igneous ocean crust that transports "fluid-mobile" elements, such as barium (Ba), and a sediment melt that supplies thorium (Th) and the light rare earth elements. This two-component framework has been widely called upon to explain global geochemical trends as well as geochemical variations within individual arcs, such as the Marianas. Here, we show that this paradigm is inconsistent with mass balance, due to the low Ba contents of igneous ocean crust, and with experimental data, which show that aqueous fluids from the igneous oceanic crust would be too dilute to substantially affect arc compositions. Observations previously attributed to the sediment melt/igneous-crust-fluid hypothesis are better explained by diverse subducting sediment compositions coupled with ambient mantle wedge heterogeneity, both globally and for the Marianas.Publication Competing climate feedbacks of ice sheet freshwater discharge in a warming world(2024) DeConto, Robert; Pollard, DavidFreshwater discharge from ice sheets induces surface atmospheric cooling and subsurface ocean warming, which are associated with negative and positive feedbacks respectively. However, uncertainties persist regarding these feedbacks' relative strength and combined effect. Here we assess associated feedbacks in a coupled ice sheet-climate model, and show that for the Antarctic Ice Sheet the positive feedback dominates in moderate future warming scenarios and in the early stage of ice sheet retreat, but is overwhelmed by the negative feedback in intensive warming scenarios when the West Antarctic Ice Sheet undergoes catastrophic collapse. The Atlantic Meridional Overturning Circulation is affected by freshwater discharge from both the Greenland and the Antarctic ice sheets and, as an interhemispheric teleconnection bridge, exacerbates the opposing ice sheet's retreat via the Bipolar Seesaw. These results highlight the crucial role of ice sheet-climate interactions via freshwater flux in future ice sheet retreat and associated sea-level rise. Ice sheet freshwater discharge interacts with the climate and affects the ice sheet's sensitivity to climate change. This study shows that the overall feedback shifts from positive to negative as the pace of future warming intensifiesPublication Pliocene-Pleistocene warm-water incursions and water mass changes on the Ross Sea continental shelf (Antarctica) based on foraminifera from IODP Expedition 374(2024) Leckie, R. Mark; Seidenstein, Julia; McKay, Robert; De Santis, Laura; Harwood, DavidInternational Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to reconstruct paleoenvironments, track the history of key water masses, and assess model simulations that show warm-water incursions from the Southern Ocean led to the loss of marine-based Antarctic ice sheets during past interglacials. IODP Site U1523 (water depth 828 m) is located at the continental shelf break, northeast of Pennell Bank on the southeastern flank of Iselin Bank, where it lies beneath the Antarctic Slope Current (ASC). This site is sensitive to warm-water incursions from the Ross Sea Gyre and modified Circumpolar Deep Water (mCDW) today and during times of past warming climate. Multiple incursions of subpolar or temperate planktic foraminifera taxa occurred at Site U1523 after 3.8 Ma and prior to similar to 1.82 Ma. Many of these warm-water taxa incursions likely represent interglacials of the latest Early Pliocene and Early Pleistocene, including Marine Isotope Stage (MIS) Gi7 to Gi3 (similar to 3.72-3.65 Ma), and Early Pleistocene MIS 91 or 90 (similar to 2.34-2.32 Ma) and MIS 77-67 (similar to 2.03-1.83 Ma) and suggest warmer-than-present conditions and less ice cover in the Ross Sea. However, a moderately resolved age model based on four key events prohibits us from precisely correlating with Marine Isotope Stages established by the LR04 Stack; therefore, these correlations are best estimates. Diatom-rich intervals during the latest Pliocene at Site U1523 include evidence of anomalously warm conditions based on the presence of subtropical and temperate planktic foraminiferal species in what likely correlates with interglacial MIS G17 (similar to 2.95 Ma), and a second interval that likely correlates with MIS KM3 (similar to 3.16 Ma) of the mid-Piacenzian Warm Period. Collectively, these multiple incursions of warmer-water planktic foraminifera provide evidence for polar amplification during super-interglacials of the Pliocene and Early Pleistocene. Higher abundances of planktic and benthic foraminifera during the Mid- to Late Pleistocene associated with interglacials of the MIS 37-31 interval (similar to 1.23-1.07 Ma), MIS 25 (similar to 0.95 Ma), MIS 15 (similar to 0.60 Ma), and MIS 6-5e transition (similar to 0.133-0.126 Ma) also indicate a reduced ice shelf and relatively warm conditions, including multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). A decrease in sedimentation rate after similar to 1.78 Ma is followed by a major change in benthic foraminiferal biofacies marked by a decrease in Globocassidulina subglobosa and a decrease in mud (< 63 m) after similar to 1.5 Ma. Subsequent dominance of Trifarina earlandi biofacies beginning during MIS 15 (similar to 600 ka) indicate progressive strengthening of the Antarctic Slope Current along the shelf edge of the Ross Sea during the mid to Late Pleistocene. A sharp increase in foraminiferal fragmentation after the MPT (similar to 900 ka) and variable abundances of T. earlandi indicate higher productivity, a stronger but variable ASC during interglacials, and/or corrosive waters, suggesting changes in water masses entering (mCDW) and exiting (High Salinity Shelf Water or Dense Shelf Water) the Ross Sea since the MPT.Publication Freshwater inflows to closed basins of the Andean plateau in Chile, Argentina, and Bolivia(2025) Moran, Brendan J.; Kirshen, Alexander B; Munk, Lee Ann; Russo, Aeon A; Mcknight, Sarah V; Jenckes, Jordan; Corkran, Daniel B; Breesee, Magdalen; Boutt, DavidMore than half the world's lithium resources are found in brine aquifers in Chile, Argentina, and Bolivia. Lithium brine processing requires freshwater, so as lithium exploration increases, accurate estimates of freshwater availability are critical for water management decisions in this region with limited water resources. Here we calculate modern freshwater inflows, such as groundwater recharge and streamflow, for 28 active or prospective lithium-producing basins. We use regional water budget assessments, field streamflow measurements, and global climate and groundwater recharge datasets. Using the freshwater inflow estimates, we calculate water scarcity using the Available Water Remaining methodology. Among all 28 basins, freshwater inflows range from 2 to 33 mm year-1. Our results reveal that commonly used global hydrologic models overestimate streamflow and freshwater availability substantially, leading to inaccurate water scarcity classifications.Publication Contemporary and relic waters strongly decoupled in arid alpine environments(2024) Moran, Brendan J.; Boutt, David; Munk, Lee Ann; Fisher, Joshua DDeciphering the dominant controls on the connections between groundwater, surface water, and climate is critical to understanding water cycles in arid environments. Yet, persistent uncertainties in the fundamental hydrology of these systems remain. The growing demand for critical minerals such as lithium and associated water demands in the arid environments in which they often occur has amplified the urgency to address these uncertainties. We present an integrated hydrological analysis of the Dry Andes region utilizing a uniquely comprehensive set of tracer data (3H, 18O/2H) for these environments, paired directly with physical hydrological observations. We find two strongly decoupled hydrological systems that interact only under specific hydrogeological conditions where preferential conduits exist. The primary conditions creating these conduits are laterally extensive fine-grained evaporite and/or lacustrine units and perennial flowing streams connected with regional groundwater discharge sites. The efficient capture and transport of modern or “contemporary” water (weeks to years old) within these conduits is the primary control of the interplay between modern hydroclimate variations and groundwater aquifers in these environments. Modern waters account for a small portion of basin budgets but are critical to sustaining surface waters due to the existence of these conduits. As a result, surface waters near basin floors are disproportionally sensitive to short-term climate and anthropogenic perturbations. The framework we present describes a new understanding of the dominant controls on natural water cycles intrinsic to these arid high-elevation systems that will improve our ability to manage critical water resources.Publication Contemporary and relic waters strongly decoupled in arid alpine environments(2024) Moran, Brendan J.; Boutt, David; Munk, LeeAnn; Fisher, Joshua DDeciphering the dominant controls on the connections between groundwater, surface water, and climate is critical to understanding water cycles in arid environments. Yet, persistent uncertainties in the fundamental hydrology of these systems remain. The growing demand for critical minerals such as lithium and associated water demands in the arid environments in which they often occur has amplified the urgency to address these uncertainties. We present an integrated hydrological analysis of the Dry Andes region utilizing a uniquely comprehensive set of tracer data (3H, 18O/2H) for these environments, paired directly with physical hydrological observations. We find two strongly decoupled hydrological systems that interact only under specific hydrogeological conditions where preferential conduits exist. The primary conditions creating these conduits are laterally extensive fine-grained evaporite and/or lacustrine units and perennial flowing streams connected with regional groundwater discharge sites. The efficient capture and transport of modern or "contemporary" water (weeks to years old) within these conduits is the primary control of the interplay between modern hydroclimate variations and groundwater aquifers in these environments. Modern waters account for a small portion of basin budgets but are critical to sustaining surface waters due to the existence of these conduits. As a result, surface waters near basin floors are disproportionally sensitive to short-term climate and anthropogenic perturbations. The framework we present describes a new understanding of the dominant controls on natural water cycles intrinsic to these arid high-elevation systems that will improve our ability to manage critical water resources.Publication Contemporary and relic waters strongly decoupled in arid alpine environments(2024) Moran, Brendan J.; Boutt, David F; Munk, Lee Ann; Fisher, Joshua D.Deciphering the dominant controls on the connections between groundwater, surface water, and climate is critical to understanding water cycles in arid environments. Yet, persistent uncertainties in the fundamental hydrology of these systems remain. The growing demand for critical minerals such as lithium and associated water demands in the arid environments in which they often occur has amplified the urgency to address these uncertainties. We present an integrated hydrological analysis of the Dry Andes region utilizing a uniquely comprehensive set of tracer data (3H, 18O/2H) for these environments, paired directly with physical hydrological observations. We find two strongly decoupled hydrological systems that interact only under specific hydrogeological conditions where preferential conduits exist. The primary conditions creating these conduits are laterally extensive fine-grained evaporite and/or lacustrine units and perennial flowing streams connected with regional groundwater discharge sites. The efficient capture and transport of modern or “contemporary” water (weeks to years old) within these conduits is the primary control of the interplay between modern hydroclimate variations and groundwater aquifers in these environments. Modern waters account for a small portion of basin budgets but are critical to sustaining surface waters due to the existence of these conduits. As a result, surface waters near basin floors are disproportionally sensitive to short-term climate and anthropogenic perturbations. The framework we present describes a new understanding of the dominant controls on natural water cycles intrinsic to these arid high-elevation systems that will improve our ability to manage critical water resources.Publication Contemporary and relic waters strongly decoupled in arid alpine environments(2024) Moran, Brendan J.; Boutt, David; Munk, Lee Ann; Fisher, Joshua D.Deciphering the dominant controls on the connections between groundwater, surface water, and climate is critical to understanding water cycles in arid environments. Yet, persistent uncertainties in the fundamental hydrology of these systems remain. The growing demand for critical minerals such as lithium and associated water demands in the arid environments in which they often occur has amplified the urgency to address these uncertainties. We present an integrated hydrological analysis of the Dry Andes region utilizing a uniquely comprehensive set of tracer data (3H, 18O/2H) for these environments, paired directly with physical hydrological observations. We find two strongly decoupled hydrological systems that interact only under specific hydrogeological conditions where preferential conduits exist. The primary conditions creating these conduits are laterally extensive fine-grained evaporite and/or lacustrine units and perennial flowing streams connected with regional groundwater discharge sites. The efficient capture and transport of modern or “contemporary” water (weeks to years old) within these conduits is the primary control of the interplay between modern hydroclimate variations and groundwater aquifers in these environments. Modern waters account for a small portion of basin budgets but are critical to sustaining surface waters due to the existence of these conduits. As a result, surface waters near basin floors are disproportionally sensitive to short-term climate and anthropogenic perturbations. The framework we present describes a new understanding of the dominant controls on natural water cycles intrinsic to these arid high-elevation systems that will improve our ability to manage critical water resources.Publication Geoprivacy knowledge, attitudes, and behaviors in contemporary China(Taylor & Francis, 2024-11-14) Zhang, Hongyu; McKenzie, GrantChina has an Internet penetration rate of over 70 percent and a massive user base of social media. However, the topic of privacy attitudes among Chinese individuals remains understudied. We analyzed geoprivacy concerns in China through an online survey and regression analysis. Our findings suggest a positive relation among privacy knowledge, attitude, and behavior, consistent with related literature. Declarative knowledge (such as privacy rights), on the other hand, was found to have a negative relation with privacy concerns, which has not been reported previously. In terms of demographic moderators, females had less privacy knowledge but more privacy protection behaviors, while the impact of age on privacy concerns was inconclusive. A notable discovery was the regional difference in privacy concerns within China, suggesting the potential geopolitical influence on individuals’ values and beliefs. Combined with the uncovering of behavioral change in response to involuntary location disclosure, the results of this article challenge the conventional notion that Chinese individuals are indifferent to their online privacy, thus reintroducing an underexplored perspective from the Global South into geoprivacy studies.Publication Timing and Pacing of Indonesian Throughflow Restriction and Its Connection to Late Pliocene Climate Shifts(2019-01-01) Auer, Gerald; De Vleeschouwer, David; Smith, Rebecca A.; Bogus, Kara; Groeneveld, Jeroen; Grunert, Patrick; Castañeda, Isla S.; Petrick, Benjamin; Christensen, Beth; Fulthorpe, Craig; Gallagher, Stephen J.; Henderiks, Jorijntjedrier conditions. This shift fundamentally reorganized Earth's climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned high‐resolution sediment geochemistry, calcareous nannofossil, and X‐ray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogue‐based interpretations of nannofossil assemblages indicate that ITF configuration culminated ~3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (~3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the Sahul‐Indian Ocean Bjerknes mechanism and increased the response to glacio‐eustatic variability.Publication Impact of climate change on New York City’s coastal flood hazard: Increasing flood heights from the preindustrial to 2300 CE(2017-01-01) Garner, Andra J.; Mann, Michael E.; Emanuel, Kerry A.; Kopp, Robert E.; Lin, Ning; Alley, Richard B.; Horton, Benjamin P.; Deconto, Robert M; Donnelly, Jeffrey P.; Pollard, DavidThe flood hazard in New York City depends on both storm surges and rising sea levels. We combine modeled storm surges with probabilistic sea-level rise projections to assess future coastal inundation in New York City from the preindustrial era through 2300 CE. The storm surges are derived from large sets of synthetic tropical cyclones, downscaled from RCP8.5 simulations from three CMIP5 models. The sea-level rise projections account for potential partial collapse of the Antarctic ice sheet in assessing future coastal inundation. CMIP5 models indicate that there will be minimal change in storm-surge heights from 2010 to 2100 or 2300, because the predicted strengthening of the strongest storms will be compensated by storm tracks moving offshore at the latitude of New York City. However, projected sea-level rise causes overall flood heights associated with tropical cyclones in New York City in coming centuries to increase greatly compared with preindustrial or modern flood heights. For the various sea-level rise scenarios we consider, the 1-in-500-y flood event increases from 3.4 m above mean tidal level during 1970–2005 to 4.0–5.1 m above mean tidal level by 2080–2100 and ranges from 5.0–15.4 m above mean tidal level by 2280–2300. Further, we find that the return period of a 2.25-m flood has decreased from ∼500 y before 1800 to ∼25 y during 1970–2005 and further decreases to ∼5 y by 2030–2045 in 95% of our simulations. The 2.25-m flood height is permanently exceeded by 2280–2300 for scenarios that include Antarctica’s potential partial collapse.Publication Reconstructing Holocene Glacier and Climate Fluctuations From Lake Sediments in Vårfluesjøen, Northern Spitsbergen(2018-01-01) Røthe, Torgeir O.; Bakke, Jostein; Støren, Eivind W. N.; Bradley, Raymond S.A process-based understanding of lacustrine deposited sediments in Arctic lakes is essential to set the present warming and hydroclimatic shift into perspective. From such a perspective, we can enhance our understanding of the natural climate variability in the Arctic. Here, we present work from the northern coast of Spitsbergen in which we unravel the sediment sequence from a distal glacier-fed lake, Vårfluesjøen. Utilizing recent methodological and technological developments, we base our interpretation on new tools that better visualize and characterize the sediments cores. High-resolution X-ray Computed Tomography (X-ray CT) is used to visualize the lake sediments and quantify the sand-sized particles found in the 210Pb- and radiocarbon-dated sediments, together with a multi-proxy approach including measurement of their physical, geochemical, and magnetic properties. Our findings suggest that Vårfluesjøen (6 m a.s.l.) was isolated from Woodfjorden at c. 10200 ± 260 cal. yr. BP. During the early Holocene, the glaciers in the Vårfluesjøen catchment were considerably smaller than today or had even melted completely. At the start of the Neoglacial period (c. 3500 cal. yr. BP), we find increased glacier activity in the catchment of the lake. X-ray CT reveals an increased frequency of sand-sized particles from 3500 to 1750 cal. yr. BP, suggesting greater wintertime aeolian activity. Starting c. 2250 years ago, we find a progressive increase in snowmelt runoff in the Vårfluesjøen catchment, with peak runoff from 1000 to 750 cal. yr. BP. This coincides with a drop in sand-sized particles, hence less favorable environment for aeolian activity, and implying wetter conditions. During the last 2000 years, there is evidence for high glacier activity between c. 2000 to 900 and 750–350 cal. yr. BP. In between these time spans, less activity is recorded in the periods 1900–1800, 1000–800, and 350–150 cal. yr. BP.Publication Three-dimensional variations of the slab geometry correlate with earthquake distributions at the Cascadia subduction system(2018-01-01) Gao, HaiyingSignificant along-strike variations of seismicity are observed at subduction zones, which are strongly influenced by physical properties of the plate interface and rheology of the crust and mantle lithosphere. However, the role of the oceanic side of the plate boundary on seismicity is poorly understood due to the lack of offshore instrumentations. Here tomographic results of the Cascadia subduction system, resolved with full-wave ambient noise simulation and inversion by integrating dense offshore and onshore seismic datasets, show significant variations of the oceanic lithosphere along strike and down dip from spreading centers to subduction. In central Cascadia, where seismicity is sparse, the slab is imaged as a large-scale low-velocity feature near the trench, which is attributed to a highly hydrated and strained oceanic lithosphere underlain by a layer of melts or fluids. The strong correlation suggests that the properties of the incoming oceanic plate play a significant role on seismicity.Publication Large Ensemble Modeling of the Last Deglacial Retreat of the West Antarctic Ice Sheet: Comparison of Simple and Advanced Statistical Techniques(2016-01-01) Pollard, David; Chang, Won; Haran, Murali; Applegate, Patrick; DeConto, RobertA 3-D hybrid ice-sheet model is applied to the last deglacial retreat of the West Antarctic Ice Sheet over the last ∼ 20 000 yr. A large ensemble of 625 model runs is used to calibrate the model to modern and geologic data, including reconstructed grounding lines, relative sea-level records, elevation–age data and uplift rates, with an aggregate score computed for each run that measures overall model–data misfit. Two types of statistical methods are used to analyze the large-ensemble results: simple averaging weighted by the aggregate score, and more advanced Bayesian techniques involving Gaussian process-based emulation and calibration, and Markov chain Monte Carlo. The analyses provide sea-level-rise envelopes with well-defined parametric uncertainty bounds, but the simple averaging method only provides robust results with full-factorial parameter sampling in the large ensemble. Results for best-fit parameter ranges and envelopes of equivalent sea-level rise with the simple averaging method agree well with the more advanced techniques. Best-fit parameter ranges confirm earlier values expected from prior model tuning, including large basal sliding coefficients on modern ocean beds.Publication Impacts of Carbonate Buffering on Atmospheric Equilibration of CO2, δ13CDIC, and Δ14CDIC in Rivers and Streams(2024-01-01) Winnick, Matthew J.; Saccardi, BrianRivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO2) to the atmosphere. However, the sources of this CO2 and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO2 in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO2 and the stable and radio- isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO2 model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically-coupled 5th-order stream network. We find that carbonate buffering reactions contribute >60% of emissions in high-alkalinity, moderate groundwater-CO2 environments. However, atmosphere equilibration timescales of CO2 are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO2 across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO2 and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio- carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate-dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO2 patterns across variable alkalinities.Publication Deep learning estimation of northern hemisphere soil freeze-thaw dynamics using satellite multi-frequency microwave brightness temperature observations(2023-01-01) Rawlins, Michael A.Satellite microwave sensors are well suited for monitoring landscape freeze-thaw (FT) transitions owing to the strong brightness temperature (TB) or backscatter response to changes in liquid water abundance between predominantly frozen and thawed conditions. The FT retrieval is also a sensitive climate indicator with strong biophysical importance. However, retrieval algorithms can have difficulty distinguishing the FT status of soils from that of overlying features such as snow and vegetation, while variable land conditions can also degrade performance. Here, we applied a deep learning model using a multilayer convolutional neural network driven by AMSR2 and SMAP TB records, and trained on surface (~0–5 cm depth) soil temperature FT observations. Soil FT states were classified for the local morning (6 a.m.) and evening (6 p.m.) conditions corresponding to SMAP descending and ascending orbital overpasses, mapped to a 9 km polar grid spanning a five-year (2016–2020) record and Northern Hemisphere domain. Continuous variable estimates of the probability of frozen or thawed conditions were derived using a model cost function optimized against FT observational training data. Model results derived using combined multi-frequency (1.4, 18.7, 36.5 GHz) TBs produced the highest soil FT accuracy over other models derived using only single sensor or single frequency TB inputs. Moreover, SMAP L-band (1.4 GHz) TBs provided enhanced soil FT information and performance gain over model results derived using only AMSR2 TB inputs. The resulting soil FT classification showed favorable and consistent performance against soil FT observations from ERA5 reanalysis (mean percent accuracy, MPA: 92.7%) and in situ weather stations (MPA: 91.0%). The soil FT accuracy was generally consistent between morning and afternoon predictions and across different land covers and seasons. The model also showed better FT accuracy than ERA5 against regional weather station measurements (91.0% vs. 86.1% MPA). However, model confidence was lower in complex terrain where FT spatial heterogeneity was likely beneath the effective model grain size. Our results provide a high level of precision in mapping soil FT dynamics to improve understanding of complex seasonal transitions and their influence on ecological processes and climate feedbacks, with the potential to inform Earth system model predictions.Publication Bering Sea Surface Water Conditions during Marine Isotope Stages 12 to 10 at Navarin Canyon (IODP Site U1345)(2016-01-01) Caissie, Beth E.; Brigham-Grette, Julie; Cook, Mea S.; Colmenero-Hidalgo, ElenaRecords of past warm periods are essential for understanding interglacial climate system dynamics. Marine Isotope Stage 11 occurred from 425 to 394 ka, when global ice volume was the lowest, sea level was the highest, and terrestrial temperatures were the warmest of the last 500 kyr. Because of its extreme character, this interval has been considered an analog for the next century of climate change. The Bering Sea is ideally situated to record how opening or closing of the Pacific–Arctic Ocean gateway (Bering Strait) impacted primary productivity, sea ice, and sediment transport in the past; however, little is known about this region prior to 125 ka. IODP Expedition 323 to the Bering Sea offered the unparalleled opportunity to look in detail at time periods older than had been previously retrieved using gravity and piston cores. Here we present a multi-proxy record for Marine Isotope Stages 12 to 10 from Site U1345, located near the continental shelf-slope break. MIS 11 is bracketed by highly productive laminated intervals that may have been triggered by flooding of the Beringian shelf. Although sea ice is reduced during the early MIS 11 laminations, it remains present at the site throughout both glacials and MIS 11. High summer insolation is associated with higher productivity but colder sea surface temperatures, which implies that productivity was likely driven by increased upwelling. Multiple examples of Pacific–Atlantic teleconnections are presented including laminations deposited at the end of MIS 11 in synchrony with millennial-scale expansions in sea ice in the Bering Sea and stadial events seen in the North Atlantic. When global eustatic sea level was at its peak, a series of anomalous conditions are seen at U1345. We examine whether this is evidence for a reversal of Bering Strait throughflow, an advance of Beringian tidewater glaciers, or a turbidite.Publication Geochemical evidence for evolving Proterozoic crustal thickness and orogenic styles in southwestern Laurentia(2023-01-01) Hillenbrand, Ian W.; Williams, Michael L.It has long been challenging for researchers to track the crustal thickness and mode(s) of crustal modification in ancient convergent margins, limiting evaluation of the tectonic styles and processes that modify continental crust during orogenesis. We present trace element igneous geochemical crustal thickness proxies that quantitatively track the crustal thickness evolution of the long-lived Proterozoic active margin in the southwestern U.S.A. We integrate these results with geobarometric data to constrain the mode of crustal modification. The data indicate a complex record of crustal thickness change in space and time and evolving orogenic styles. Geochemical proxies at 1.84–1.72 Ga are consistent with 20–40 km thick magmatic arcs that were locally thickened to ∼50 km during ∼1.75 Ga tectonism. During the Yavapai orogeny, 1.72–1.69 Ga, a ∼200-km-wide belt of 50-60 km thick crust extended from southern California to northern Colorado and was rapidly thinned and exhumed by ∼1.68 Ga. Crustal thickening and thinning during the Yavapai orogeny largely occurred by shortening and exhumation, respectively, in the upper 25 km of the crust. Subsequent 1.68–1.60 Ga tectonism involved crustal growth, local crustal thickening, and low-P, high-T metamorphism, consistent with extensional accretionary orogenesis. The 1.47–1.37 Ga Picuris orogeny was associated with 50–60 km thick crust across much of the Southwest and involved crustal shortening with ∼10 km of magmatic underplating. Advective heat from the emplacement of ferroan granites in the mid-crust likely contributed to elevated geothermal gradients and rheologically weakened the crust. Our results suggest evolving orogenic styles in the Southwest from 1.75–1.69 Ga short-lived crustal thickening associated with terrane accretion to 1.69–1.60 Ga largely extensional accretionary orogenesis, and regional, long-lived crustal thickening at 1.47–1.37 Ga involving extensive basaltic underplating. Contrasting with some recent hypotheses, our data document a complex middle Proterozoic record for the Southwest that was not orogenically quiescent or tectonically stagnant but involved complex mountain building styles.Publication Regime shifts in Artic terrestrial hydrology manifested from impacts of climate warning(2024-01-01) Rawlins, Michael A.; Karmalkar, Ambarish V.Anthropogenic warming in the Arctic is causing hydrological cycle intensification and permafrost thaw, with implications for flows of water, carbon, and energy from terrestrial biomes to coastal zones. To better understand the likely impacts of these changes, we used a hydrology model driven by meteorological data from atmospheric reanalysis and two global climate models for the period 1980–2100. The hydrology model accounts for soil freeze–thaw processes and was applied across the pan-Arctic drainage basin. The simulations point to greater changes over northernmost areas of the basin underlain by permafrost and to the western Arctic. An acceleration of simulated river discharge over the recent past is commensurate with trends drawn from observations and reported in other studies. Between early-century (2000–2019) and late-century (2080–2099) periods, the model simulations indicate an increase in annual total runoff of 17 %–25 %, while the proportion of runoff emanating from subsurface pathways is projected to increase by 13 %–30 %, with the largest changes noted in summer and autumn and across areas with permafrost. Most notably, runoff contributions to river discharge shift to northern parts of the Arctic Basin that contain greater amounts of soil carbon. Each season sees an increase in subsurface runoff; spring is the only season where surface runoff dominates the rise in total runoff, and summer experiences a decline in total runoff despite an increase in the subsurface component. The greater changes that are seen in areas where permafrost exists support the notion that increased soil thaw is shifting hydrological contributions to more subsurface flow. The manifestations of warming, hydrological cycle intensification, and permafrost thaw will impact Arctic terrestrial and coastal environments through altered river flows and the materials they transport.Publication Factors influencing the diurnal spring distribution of sympatric urial and Siberian ibex in the Hindu Kush Mountains of Wakhan National Park, Afghanistan(2023-01-01) Moheb, Zalmai; Nelson, Michael F.; Ostrowski, Stephane; Zahler, Peter I.; Bowlick, Forrest J.; Fuller, Todd K.Patterns of habitat selection for sympatric urial Ovis vignei and Siberian ibex Capra sibirica are poorly known, in part because there are few places where such overlap exists. Using envelope modeling methodology, we analyzed location data of these species in the Hindu Kush range along the Wakhan Valley of the Wakhan National Park (10,950 km2) in northeastern Afghanistan, recorded during field surveys in April-May of 2011, 2015, and 2018. Distribution models showed significant ecological niche differences (P < 0.05) between urial (a true sheep species) and ibex (a true goat species) for most variables. Urial stayed at lower elevations compared to ibex, both species tended to avoid flat areas, but urial avoided slopes above 60 %. Urial used southeast-facing slopes more, and west-facing slopes less, than available, whereas ibex had a slightly more than expected use of southwest-facing slopes. Urial preferred terrains with ruggedness index (∼20–40) of the values available (15–60), whereas ibex were more generalist in terrain preference. Urial utilized habitats closer to human activity areas compared to ibex. Both species utilized the higher quality vegetation areas (NDVI > 0) and showed the same avoidance of lower quality areas. Understanding selection criteria of habitat use by urial and ibex in Wakhan Valley, inhabited by over 14,000 people and their livestock (ca. 78,000), will enable adjustments to the protection schemes regarding the requirements of two key mountain ungulate species critical to the sustainability and conservation of this unique ecosystem. This type of information is very scarce in the literature for the sympatric mountain ungulates in Asia.
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